The present invention relates generally to optical devices and more specifically to an optical phased array that electronically steers a beam of light.
Prior art phased array optical beam steering devices and methods typically limit the size of phase shifter to less than the wavelength of the light to be steered in order to achieve high performance and large-angle beam steering. However, many practical problems exist when the size of the phase shifters is small. One problem is that an extremely large number of phase shifters are required. For light having of wavelength of 1 .mu.m, if the size of phase shifter is 1 .mu.m, then 10,000 phase shifters per centimeter of array are required (neglecting the spacing between each phase shifter). Since apertures size up to one meter in diameter may be desired, the total number of phase shifters in an array may exceed 1,000,000. This results in extremely complex and expensive interconnection schemes.
Additionally, use of such small phase shifters results in inefficient use of available substrate area. For example, a typical array may include phase shifters that are 1 .mu.m in width having a separation of not less than 0.1 .mu.m between phase shifters. In such an arrangement, the space between the phase shifters is essentially wasted and represents ten percent of the available area. If the width of each phase shifter is decreased to 0.5 .mu.m, then the wasted area comprises twenty percent of the available area. Clearly, this is inefficient and wasteful.
Another more difficult problem exists. For a phase shifter having a width approximately equal to the wavelength of light, the light beam entering the phase shifter diverges as it propagates through the phase shifter. It is virtually impossible to maintain the size of the beam as it passes through the phase shifter, thus only a small portion of light eventually passes through the phase shifter while the remaining portion of the light beam travels through neighboring phase shifters. Accordingly, only a small portion of light emerging from each phase shifter has the desired phase while the remaining portion of the light emerging from neighboring phase shifters has an incorrect phase. Therefore, even if an extremely large numbers of phase shifters can be successfully integrated, the performance of the device is relatively poor. Also, since the length (or the thickness) of the phase shifter is typically about 10 .mu.m, and is much larger than the width, the edge effect is very strong. Due to the edge effect, the electric field is not uniform within the phase shifter resulting in a variation of the refractive index within the phase shifter. Therefore, even for the small portion of light passing through the phase shifter, the phase shifts are not equal.
An example of a known optical beam steering device is disclosed in U.S. Pat. No. 5,093,740 issued on Mar. 3, 1992 to Dorschner et al. This device uses phase shifters having general spacing of about one-half of the wavelength of light. This results in a one-dimensional phase shifter density of about 20,000 per centimeter, if the wavelength of the light is 1 .mu.m. The reference discloses that manufacture of sub-micron geometry is feasible but interconnecting such a large array of phase shifters appears to be a monumental task. The reference device seeks to overcome the task of interconnecting the vast number of phase shifters by dividing the array into sub-arrays interconnected in a parallel arrangement. This significantly increases the complexity and manufacturing cost of the device. Additionally, as the size of the array is increased, the number of interconnections again becomes problematic. Another problem in this prior art approach is that it limits the number of addressable beam directions to a few discrete positions due to the phase mismatch between sub-arrays.
Accordingly, it is an object of the present invention to substantially overcome the above-described problems.
It is another object of the present invention to provide a novel optical beam steering device and method having a plurality of phase shifters to steer the beam of light.
It is a further object of the present invention to provide a novel optical beam steering device having a plurality of phase shifters where the dimension of the phase shifter is much greater than the wavelength of light so that the number of connections to the array is greatly reduced.
It is also an object of the present invention to provide a novel optical beam steering device and method where a single peak beam is produced by providing irregular spacing between phase shifters.
It is still an object of the present invention to provide a novel optical beam steering device where the beam divergence within the phase shifter is minimized.
It is yet another object of the present invention to provide a novel optical beam steering device having a lens associated with each phase shifter to permit large-angle beam steering. It is still a further object of the present invention to provide an optical beam steering device and method having lenses for shifting an optical axis.